Figure 4.

Signal spatial properties and time course. (A) Signal response to a 7.7-cd/m² spot stimulus on a 0.12-cd/m² background. The NIR reflectance changes produced two predominant signals: a negative signal (N) and a positive signal (P) that were spatially adjacent. The response was localized with the stimulated retina. Scale bar, 6° of the visual angle. Arrows: superior and nasal directions in the fundus image. Inset: the stimulus used to evoke the response. (B) A horizontal line profile of the signal. The average intensity values of rectangular region in (A) are plotted as a function of pixel values from the functional image above. The negative signal shows a clear dip below baseline reflectance and, nasally adjacent, a positive signal of lesser magnitude. (C) Fractional reflectance time course of three ROIs. Both the positive (ROI P, white) and negative (ROI N, black) signals showed minimal deviation from baseline during the first 2 seconds (stimulus off). From 2 to 5 seconds (stimulus on) both signals developed and grew in magnitude. Between 5 and 10 seconds (stimulus off), the signals had a slow recovery phase back to baseline reflectance. A third ROI (O, dashed lines) is also plotted. There was minimal change in reflectance for this ROI, demonstrating the signals were tightly coupled to the stimulated retina.